beanpropertyrowmapper.java

来自「spring framework 2.5.4源代码」· Java 代码 · 共 220 行

/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */	

package org.springframework.jdbc.core;

import java.beans.PropertyDescriptor;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeanWrapper;
import org.springframework.beans.NotWritablePropertyException;
import org.springframework.beans.PropertyAccessorFactory;
import org.springframework.dao.DataRetrievalFailureException;
import org.springframework.dao.InvalidDataAccessApiUsageException;
import org.springframework.jdbc.support.JdbcUtils;
import org.springframework.util.Assert;

/**
 * {@link RowMapper} implementation that converts a row into a new instance
 * of the specified mapped target class. The mapped target class must be a
 * top-level class and it must have a default or no-arg constructor.
 *
 * <p>Column values are mapped based on matching the column name as obtained from result set
 * metadata to public setters for the corresponding properties. The names are matched either
 * directly or by transforming a name separating the parts with underscores to the same name
 * using "camel" case.
 *
 * <p>Mapping is provided for fields in the target class for many common types, e.g.:
 * String, boolean, Boolean, byte, Byte, short, Short, int, Integer, long, Long,
 * float, Float, double, Double, BigDecimal, <code>java.util.Date</code>, etc.
 *
 * <p>To facilitate mapping between columns and fields that don't have matching names,
 * try using column aliases in the SQL statement like "select fname as first_name from customer".
 *
 * <p>Please note that this class is designed to provide convenience rather than high performance.
 * For best performance consider using a custom RowMapper.
 *
 * @author Thomas Risberg
 * @author Juergen Hoeller
 * @since 2.5
 */
public class BeanPropertyRowMapper implements RowMapper {

	/** Logger available to subclasses */
	protected final Log logger = LogFactory.getLog(getClass());

	/** The class we are mapping to */
	protected Class mappedClass;

	/** Map of the fields we provide mapping for */
	private Map mappedFields;


	/**
	 * Create a new BeanPropertyRowMapper.
	 * @see #setMappedClass
	 */
	public BeanPropertyRowMapper() {
	}

	/**
	 * Create a new BeanPropertyRowMapper.
	 * @param mappedClass the class that each row should be mapped to.
	 */
	public BeanPropertyRowMapper(Class mappedClass) {
		initialize(mappedClass);
	}


	/**
	 * Set the class that each row should be mapped to.
	 */
	public void setMappedClass(Class mappedClass) {
		if (this.mappedClass == null) {
			initialize(mappedClass);
		}
		else {
			if (!this.mappedClass.equals(mappedClass)) {
				throw new InvalidDataAccessApiUsageException("The mapped class can not be reassigned to map to " +
						mappedClass + " since it is already providing mapping for " + this.mappedClass);
			}
		}
	}

	/**
	 * Initialize the mapping metadata for the given class.
	 * @param mappedClass the mapped class.
	 */
	protected void initialize(Class mappedClass) {
		this.mappedClass = mappedClass;
		this.mappedFields = new HashMap();
		PropertyDescriptor[] pds = BeanUtils.getPropertyDescriptors(mappedClass);
		for (int i = 0; i < pds.length; i++) {
			PropertyDescriptor pd = pds[i];
			if (pd.getWriteMethod() != null) {
				this.mappedFields.put(pd.getName().toLowerCase(), pd);
				String underscoredName = underscoreName(pd.getName());
				if (!pd.getName().toLowerCase().equals(underscoredName)) {
					this.mappedFields.put(underscoredName, pd);
				}
			}
		}
	}

	/**
	 * Convert a name in camelCase to an underscored name in lower case.
	 * Any upper case letters are converted to lower case with a preceding underscore.
	 * @param name the string containing original name
	 * @return the converted name
	 */
	private String underscoreName(String name) {
		StringBuffer result = new StringBuffer();
		if (name != null && name.length() > 0) {
			result.append(name.substring(0, 1).toLowerCase());
			for (int i = 1; i < name.length(); i++) {
				String s = name.substring(i, i + 1);
				if (s.equals(s.toUpperCase())) {
					result.append("_");
					result.append(s.toLowerCase());
				}
				else {
					result.append(s);
				}
			}
		}
		return result.toString();
	}

	/**
	 * Get the class that we are mapping to.
	 */
	public final Class getMappedClass() {
		return this.mappedClass;
	}


	/**
	 * Extract the values for all columns in the current row.
	 * <p>Utilizes public setters and result set metadata.
	 * @see java.sql.ResultSetMetaData
	 */
	public Object mapRow(ResultSet rs, int rowNumber) throws SQLException {
		Assert.state(this.mappedClass != null, "Mapped class was not specified");
		Object mappedObject = BeanUtils.instantiateClass(this.mappedClass);
		BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(mappedObject);
		initBeanWrapper(bw);

		ResultSetMetaData rsmd = rs.getMetaData();
		int columnCount = rsmd.getColumnCount();
		for (int index = 1; index <= columnCount; index++) {
			String column = JdbcUtils.lookupColumnName(rsmd, index).toLowerCase();
			PropertyDescriptor pd = (PropertyDescriptor) this.mappedFields.get(column);
			if (pd != null) {
				try {
					Object value = getColumnValue(rs, index, pd);
					if (logger.isDebugEnabled() && rowNumber == 0) {
						logger.debug("Mapping column '" + column + "' to property '" +
								pd.getName() + "' of type " + pd.getPropertyType());
					}
					bw.setPropertyValue(pd.getName(), value);
				}
				catch (NotWritablePropertyException ex) {
					throw new DataRetrievalFailureException(
							"Unable to map column " + column + " to property " + pd.getName(), ex);
				}
			}
		}

		return mappedObject;
	}

	/**
	 * Initialize the given BeanWrapper to be used for row mapping.
	 * To be called for each row.
	 * <p>The default implementation is empty. Can be overridden in subclasses.
	 * @param bw the BeanWrapper to initialize
	 */
	protected void initBeanWrapper(BeanWrapper bw) {
	}

	/**
	 * Retrieve a JDBC object value for the specified column.
	 * <p>The default implementation calls
	 * {@link JdbcUtils#getResultSetValue(java.sql.ResultSet, int, Class)}.
	 * Subclasses may override this to check specific value types upfront,
	 * or to post-process values return from <code>getResultSetValue</code>.
	 * @param rs is the ResultSet holding the data
	 * @param index is the column index
	 * @param pd the bean property that each result object is expected to match
	 * (or <code>null</code> if none specified)
	 * @return the Object value
	 * @throws SQLException in case of extraction failure
	 * @see org.springframework.jdbc.support.JdbcUtils#getResultSetValue(java.sql.ResultSet, int, Class)
	 */
	protected Object getColumnValue(ResultSet rs, int index, PropertyDescriptor pd) throws SQLException {
		return JdbcUtils.getResultSetValue(rs, index, pd.getPropertyType());
	}

}